This invention relates to the removal of suspended solids from waste or process streams. It is suitable for use on streams of untreated waste, primary treated waste or secondary treated waste and can provide an effluent stream which can be returned to its source or recycled for further clarification and treatment. Use of the apparatus and method on waste streams also results in a retained solids stream which can be recycled back to a treatment stage for further clarification. A recyclable separate matte or solids stream is a third product stream of the apparatus and method when used on waste streams.
A process stream containing suspended solids, such as a white water stream from a papermaking machine or a beer stream having excess disbursed carbohydrate solids can also be treated by the apparatus and method of the invention. The products of treatment of a process stream, if so treated, are: a clarified stream which is either an end or intermediate product, a retained solids stream which may be recycled or in some cases further concentrated to produce an end product, or a separate matte stream which either may be recycled or in some cases may be the desired product.
In the case where the apparatus and method are used for removing suspended solids from waste streams, the benefits of high flow rates and a three-stream yield lower the filter surface area required. This provides the ability to process large waste streams within a smaller area and therefore at lower cost. Moreover, the apparatus and method of the invention has the ability to separate large particles such as polyethylene from small particles which might be suspended in the stream. Because of the nature of the foam filtering material and the apparatus and method combination which includes its use, only a low pressure head is required to pass the stream through the filter element. In many cases this will eliminate the need for vacuum equipment, pressurization of the stream or the provision of other complex means and procedures to create a flow through the filter. In those situations where vacuum and pressure equipment are utilized, they may be more efficiently employed by use of the apparatus and method of the invention. For instance, even a slight evacuation of the interior of the apparatus greatly enhances flow rates through the foam filter material.
A further example of the advantages of the apparatus and method of the invention will be seen to result from the novel manner in which the filter medium capacity is recovered or regenerated. To this end, an apparatus and procedure for maintaining the foam area in a substantially liquid filled condition to avoid vapor lock during expansion of the area from the compressed state is employed.
In the case where the invention is utilized as an apparatus for clarification of process streams or for concentrating suspended solids, the advantage of high flow rate is also important. Of primary importance, however, is the ability and method of the apparatus to separate the process stream into three product streams, namely, a clarified stream, a small solids stream and a large solids stream. Again, this is accomplished with a simplicity of equipment made possible by both the low pressure head required to flow the stream through the filter element and the excellent recoverability of the filter medium.
The apparatus and method of the invention may be used either for filtration or classification. It can separate large particles, small particles and hydrogel from the same stream. The apparatus and method can proceed continuously, semi-continuously or on a batch or static basis. It is applicable for use in the tertiary treatment of waste water and/or between the primary and secondary waste treatments. It can separate and concentrate solids, and provide the clarification of liquid and the recycling of solids therefrom. It has application both as an addition to current separation equipment or as a replacement of current equipment.
A related application is entitled "Method of Removing Fine Suspended Solids From Effluent Streams," Ser. No. 154,800, filed May 30, 1980 by Henry A. Fremont and assigned to the same assignee as the instant application. Certain procedures of the prior art analogous to, but not teaching the instant novel apparatus and method are disclosed in Pulp and Paper Manufacture, Volume 3, First Edition, entitled "Manufacture and Testing of Paper and Board," McGraw Hill Book Company, Inc., 1953, pages 28-53.
Cellular plastic foams for use as filter elements in the apparatus and method of the invention have been known previously and such technology has been the subject of sales brochures of Crofton, Inc. of Marian, Ind., for example. Typical of the specific materials used for filter foam are those sold by Scott Paper Company, Foam Division, Chester, Pa. The Scott filter foam is a completely open cell polyester-polyurethane foam. A more detailed disclosure of suitable foams for the apparatus and method of this invention will be found in the above-mentioned application, Ser. No. 154,800.